The Past Simple denotes an action performed within a period of time which is already over.The action is cut off from the present. The time of the action may be indicated by adverbials of past time, such as yesterday, a week ago, last year, etc. e.g. The sun came out a moment ago. He made an entry in his diary every night. The Present Perfect denotes a completed action connected with the present. It is frequently used with the adverbs just, already, of late. It is also used in adverbial clauses of time after the conjunctions when, till, until, before, as soon as to denote an action completed before a definite moment in the future. e.g. I have just written to him. How many pages have you translated for today? I am not going till you have answered me. The Past Perfect denotes an action completed before a certain moment in the past. The moment may be indicated by another past action expressed by a verb in the Past simple or by another adverbial phrase. e.g. After she had cried out, she felt easier. He had not written a line since he arrived.

simple past: you know WHEN event happened present perfect: you don't know when, but event in past has effect on present. past perfect: event happened before other past event.

You use present perfect to describe/explain now, ie. the present results of the past action. Even though you put a past action in the grammar pattern, you will never use it in a past context. Past simple and past perfect are used when telling a story in the past. Use past simple for the basic events of the story, and past perfect to fill in the explanations, history and general background of the simple action. Between the two tenses, past perfect happened first, no matter in which order the actions are reported. Again, it's an earlier action used to describe a later event. You'll never use past perfect on its own.